1. Field of the Invention
The present disclosure relates to recording media and, more particularly, to recording media with eight to fourteen modulation (EFM) demodulation.
2. Description of the Related Art
Techniques of digitalizing a video signal, storing the digital video signal in a recording medium, and reproducing the digital video signal recorded in the recording medium have been studied. In general, a video signal has a much larger quantity of information than the quantity of information of an audio signal. Thus, a recording medium for storing the video signal requires a larger capacity and higher operating speed. In addition, the video signal needs to be compressed.
Attention has been focused on a digital versatile (or video) disc (DVD) technology because the DVD provides a picture quality and reproducing time better than those of a CD-ROM. Furthermore, Joint Photographic Experts Group (JPEG) and Moving Picture Experts Group (MPEG) versions 1 and 2 are well known in the art as techniques for compressing video signals and storing the compressed video signals in a recording medium such as a DVD.
A data format for the DVD is different from a data format for the CD-ROM. The data format for the DVD includes a sector composed of predetermined digital signal units. The sector is divided into a plurality of frames, such as 26 frames, for example. Each of the frames includes a synchronous signal in addition to a modulated digital video signal and an error correction code.
FIG. 1 illustrates the data format of a DVD or DVD-R/RW indicated generally by the reference numeral 100. Referring to FIG. 1, an ECC block 110, which is a logical read unit, has 16 sectors. Each of the sectors is divided into 26 synchronization frames including 0th synchronization frame through 25th synchronization frame. Each of the frames has a synchronization part SYNC and a data part. The data part is divided into a 16-byte sub data region and a 69- to 70-byte main data region. The sub data region includes a sector number, a 4-byte ID region representing information of the layer and region of the sector, a 2-byte IED region representing a parity for detecting an error of ID, a 6-byte CPR_MAI region representing system reservation data such as copy guard information, and a 4-byte buffering region allocated for overcoming restrictions caused by accurate control of a spindle motor according to a DVD recording specification.
In the case of an incremental recording mode of the DVD-R and DVD-RW, that is, when data transmission is instantaneously interrupted or new data is recorded following previous data, a linking scheme that allocates a predetermined number of bytes, such as three bytes, to a buffering region of the next recording starting point is used. Accordingly, the fifteenth byte through seventeenth byte of the buffering region becomes a linking region.
Since constant linear velocity (CLV) is employed as a method of controlling the driving of a DVD, it is required to recover a channel clock signal of a frequency corresponding to a bit period of a signal reproduced from the DVD by an optical system in order to demodulate the reproduced signal. The channel clock signal is recovered by a phase locked loop (PLL). The channel clock signal is recovered by inputting a signal read from the disc to the PLL.
FIG. 2 illustrates the order of demodulating eight to fourteen modulation (EFM) input data read from a DVD, as indicated generally by the reference numeral 200. Referring to FIG. 2, a frame synchronization signal FrameSync of the EFM data is detected in response to a channel clock signal recovered by a PLL circuit, as indicated by portion A. A frame counter is reset to zero in response to the detected frame synchronization signal. The frame counter is increased by one for each channel clock. Whenever the frame counter value becomes 16, that is, whenever lower 4 bits are 0000, a value matched with 16-bit data is obtained from a look-up table and EFM+ demodulation is carried out 91 times, as indicated by portion B. When the frame synchronization signal is detected again, the operation of resetting the frame counter, increasing the frame counter by one for each channel clock and performing the EFM+ demodulation whenever the frame counter value becomes 16 is repeated.
The EFM+ demodulation can be carried out without having an error only when the EFM data and the channel clock signal are correctly aligned with each other. If the channel clock signal leads the EFM data by one clock, that is, when the frame counter value is increased by more than +1 or the EFM input data is misaligned by one channel clock, a modulation point mismatch results in erroneous demodulation.
After a defect point caused by damage on the surface a disc, the operation of a clock recovery phase locked loop is out of a normal state. Accordingly, a channel clock frequency is increased or decreased and thus the frame counter value becomes inaccurate. As a result, a maximum of 91 erroneous demodulations of EFM data occur in a single frame.
Therefore, a device and method are desired for adaptively correcting a demodulation point to reproduce digital flash media (DFM) data, for example, when the channel clock is misaligned with the EFM data.